<!DOCTYPE html>
<html>
  <head>
    <style>
      div { color: green; }
      div:empty { color: red; }
    </style>
    <script>
      window.onload = function () {
        document.getElementById("x").appendChild(document.createTextNode("This should be green"));
      }
    </script>
  </head>
  <body>
    <div id="x"></div>
  </body>
</html>
